There are already switching modules of the input type described, in which the switch is composed of PIN diodes and is therefore current controlled. Here, low-pass filters are used, which are integrated into a LTCC multi-layer ceramic with 10 to 15 ceramic layers. These switching modules are used as multi-band front-end modules for mobile telephones and have a receiver and transmitter input for at least two different frequency bands in each case.
These kinds of conventional switching modules fulfill the following different functions:
Function 1: Connection of the frequency bands used to an antenna
Function 2: Selection of frequency band
Function 3: Selection between transmitting and receiving
Function 4: Filtering of the signals coming from a power amplifier
Function 5: Filtering of the signals received via the antenna
Functions 1 and 2 are performed by a diplexer that is composed of passive components and is integrated into the passive module. Function 3 is performed by selector switches that are created using PIN diodes. The filtering of the signals coming from the amplifiers is done by low-pass or band-pass filters; monolithic microwave ceramic, LC-filters, SAW (surface acoustic wave) and/or BAW (bulk acoustic wave) band-pass filters are used for Function 5.
The conventional switching modules have the disadvantage that the diode switches used need switching power of up to 10 mA, which because of the accumulator power required for this, primarily affects the maximum speaking time for the mobile phone.
The conventional switching module also has the disadvantage of a high insertion loss which adds up to higher losses (in some cases >1.0 dB) mainly as a result of the large number of passive components needed for the diplexer, such as coils and capacitors together with diodes forming the selector switch and together with the transmitter filters.
The conventional switching module has the further disadvantage that due to the different selection functions, firstly between transmitting and receiving and secondly between the frequency bands, a large number of passive components are integrated in the passive module, which leads to high losses and limits the extent to which the conventional module can be miniaturized.
In addition, the use of diodes entails the need for additional passive components such as voltage multipliers or capacitors.
In addition, conventional switching modules have the disadvantage that, due to the large number of passive components, the multi-layer ceramic passive module is very complex and accordingly requires more development time and is not very flexible in adjusting to altered specifications. The complexity of the passive module and its size are also increased by the transformation lines that are required for the PIN diode to work.
The conventional switching modules also have the disadvantage that integrating a large number of different frequency bands or a corresponding switchover function is not possible for reasons of space because of the fact that for each switchover function, two diodes are needed.
There are also already switching modules of the input type referred to at the beginning, in which a gallium arsenide switch is attached to a laminate. The low-pass filters are here attached to the laminate as discrete components next to the switch.
These switching modules have the disadvantage that they require a great deal of space and must therefore be configured externally on the mobile phone board.